1. Field of the Invention
The embodiments discussed herein relate to a semiconductor device including a power semiconductor element for controlling a motor or the like.
2. Background of the Related Art
Many motors and many semiconductor devices for switching-controlling them are mounted on an automobile. For such semiconductor devices, an improvement in the reliability associated with a reduction in size and an increase in environmental temperature is needed. For the purpose of achieving a reduction in size and higher reliability of the semiconductor device, one chip or one package of a power semiconductor element and a driver circuit for driving this power semiconductor element has been developed. The driver circuit includes a control circuit and a protection circuit for protecting the power semiconductor element. The protection circuit monitors an overheat state of the power semiconductor element, for example, and will notify, upon detecting the overheat state, the control circuit of this state. The control circuit will perform, upon notification of the overheat state of the power semiconductor element from the protection circuit, control for turning off the power semiconductor element, for example. The semiconductor device also includes an overcurrent limiting circuit which monitors the current flowing in the power semiconductor element. This overcurrent limiting circuit includes a circuit which indirectly detects the current flowing in the power semiconductor element and limits, when the detected current value exceeds a set overcurrent limit value, the current flowing in the power semiconductor element (e.g., see Japanese Laid-open Patent Publication No. 11-195971).
Here, in a semiconductor device which switching-controls an inductive load such as a motor, a rush current flows when the motor is activated. That is, if a power semiconductor element is turned on, the current starts to flow in the power semiconductor element and the motor. At this time, the current which initially flows results in a current having a larger current value than a current flowing during the steady operation and then the current gradually decreases and settles to a stable rated current. Here, the large current which flows prior to reaching this rated current is the rush current. Therefore, the power semiconductor element is, when it is turned on, controlled so as to be able to supply to the motor a current determined taking into consideration such a rush current.
If a load causes a short-circuit failure when it is being driven under the rated current, a current larger than at least the rush current will continue to flow in the power semiconductor element, and therefore the temperature of the power semiconductor element will abruptly rise. In this case, until the protection circuit detects an overheat state and starts protecting the power semiconductor element, the temperature of the power semiconductor element may rise to a temperature at which it is thermally destroyed. Moreover, the flowing of such a large current might cause the burnout of a wiring substrate and the malfunction or the like of a peripheral device due to a fluctuation of the power-supply voltage. Note that, also in the semiconductor device with a built-in overcurrent limiting circuit, the overcurrent limit value is set larger than the peak value of the rush current. Therefore, if the load is shorted, a current having a current value larger than the peak value of the rush current will continue to flow in the power semiconductor element. Also in this case, because the temperature of the power semiconductor element abruptly rises, the power semiconductor element has problems, such as being thermally destroyed due to an abrupt increase in temperature.